There have been developed techniques for measuring a transmission delay in communication in a flow control device at a higher level than a packet transfer device. One of the techniques is a system which is configured of an OpenFlow controller (OFC) as flow control device and an OpenFlow switch (OFS) as packet transfer device by use of OpenFlow and in which the OFC measures a transmission delay in the OFS between two points (see PTL 1 and NPLs 1 and 2).
OpenFlow is a technique in which communication is assumed as end-to-end flow and control such as path control, failure recovery, load distribution or optimization is conducted in units of flow. A flow is identified communication in combination of items of information obtained when the switch receives a packet. For example, flows, which have the same transmission source/transmission destination based on internet protocol (IP) header information and different transmission control protocol (TCP) port numbers, can be handled as different flows. For example, flows, which have the same packet information and different reception physical ports, can be handled as different flows. Communication is managed in units of flow thereby to realize control and management over independent layers. The OFS specified in NPL 2 includes a secure channel for communication with the OFC. Further, the OFS operates according to a flow table. The flow table is added or rewritten in response to an instruction from the OFC via the secure channel. The flow table defines therein a set of matching rule (header field) collated with packet header, flow statistical information (Counters), and action defining processing contents per flow. The OFS has a function of notifying reception of a packet to the OFC. A relevant matching rule may not be present in the flow table as a cause of the notification. Further, a matching rule may be present in the flow table and notification to the OFC may be designated in the action as other cause of the notification. A form of the notification message employs a Packet-in message defined in OpenFlow Protocol (OFP). The message may include part of a packet including the header information of the packet of cause, or the entirety thereof.
With the system in PTL 1, the OFC controls OFSs to be measured at two points. Specifically, the OFC controls the OFS at the start point to transmit a transmission delay measurement packet to the OFS at the end point by use of a Packet-out message in OFP. Further, the OFS controls the OFS at the end point to notify reception of the transmission delay measurement packet to the OFC. The OFC measures a time when the Packet-out is transmitted and a time when the transmission delay measurement packet reception notification is made, and manages them as transmission delay information between the two points, thereby finding a communication path with less delay. Further, the transmission delay measurement is bi-directionally made between the two points, thereby measuring round trip time (RTT) between the two points.
PTL 2 discloses therein, not an OpenFlow technique, a delay time measurement device which is connected to a packet relay device for relaying packets transmitted between terminals and is directed for measuring a transmission delay time between the terminals and the packet relay device.
Specifically, when a packet to be relayed is a real-time transport control protocol (RTCP) packet, the packet relay device outputs a copy of the RTCP packet to a computer. The computer obtains a packet reception time each time a copy of the RTCP packet is input therein, and calculates a round-trip transmission delay time based on the obtained reception time.